The tandem type of master cylinder has a plurality of hydraulic chambers which are connected to a plurality of wheel cylinders with a plurality of systems of hydraulic passages. When a driver operates a brake pedal, a hydraulic pressure is generated in a plurality of the hydraulic chambers. The hydraulic pressure is cut off not to directly operate a plurality of the wheel cylinders, but hydraulic pressures are generated in a plurality of hydraulic chambers in consideration of other physical quantities in addition to the operation quantity of the brake pedal, in order to operate a plurality of wheel cylinders. Such a braking system is so called brake-by-wire (BBW), and a braking device for this braking system has been proposed (for example, see patent document 1).